RADIATION, THE COÖRDINATE FORCE WITH GRAVITATION IN THE CONTINUOUS PROCESS OF FORMING AND DISINTEGRATING HEAVENLY BODIES-BOMBARDMENT BY METEORS THE CAUSE OF THE "CRATERS ON THE MOON T THE NEW THEORIES OF NEBULAR AND SOLAR PHENOMENA BY WILLIAM BAYARD HALE HE discovery by Sir Isaac Newton of the law of gravitation made possible the beginnings of a science of astronomy. Thenceforth it was possible was possible not merely to catalogue the stars and observe their movements, but to frame theories regarding the operation of the world-machine. The principle of gravitation furnished a key to the behavior of the planets, moons, and comets, and threw some light on the movements of bodies beyond our solar system. But is gravitation the only great law that is at work in the heavens apart from the ordinary principles of chemistry and physics? There is a fact about Newton's law which until very recently has almost escaped notice: it ceases to act when a body grows very small. As a body dwindles. into a mere particle, the proportion of mass to surface diminishes. Gravitation acts on masses. Surfaces are acted on by another force. There is a point of size below which a body passes out of the domination of gravitation and comes under the influence of another great law. The other law is that of radiation. Opposed to the force that tends to draw masses together is another force which we may call radial energy, and the effect of this second force is to drive particles away. It has long been suspected that light exerts pressure. So long as men held the old corpuscular theory of light — namely, that light consisted of actual particles projected in all directions from the source of illumination-it was easy for them Photographed at the Yerkes Observatory by Ritchey, with the s-foot reflector THE GREAT NEBULA IN ANDROMEDA THE ANDROMEDA NEBULA OCCUPIES AN AREA IN THE SKY THOUSANDS OF TIMES GREATER THAN THAT OF OUR ENTIRE SOLAR SYSTEM, MILLIONS OF TIMES THAT OF OUR SUN. SOME ASTRONOMERS CONSIDER IT NOT A TRUE NEBULA, BUT A PRODIGIOUS ASSEMBLY OF FULLY FORMED SUNS ENORMOUSLY DISTANT, FORMING A SORT OF UNIVERSE ITSELF BEYOND OUR STARS to think of it as a bombardment. Kepler, who three hundred years ago noticed how the tails of comets are repelled by the sun, theorized that the tails consisted of particles of the comet carried off by the light corpuscles as they hit the sides of the comet. His explanation may be a trifle crude, in the light of modern knowledge, yet he was essentially right. Even after the wave theory of light had |